Biaxially oriented polypropylene (BOPP) and biaxially oriented polyester (BOPET) films are used for packaging, decorative, balloon and label applications and often perform multiple functions. In label uses they typically occur in a laminated structure to provide printability, and may have transparent or matte appearance, or slip properties. In packaging uses these films sometimes form a base layer in a multilayer composite to provide structural integrity for containment function. The base layer also can support the other layers that have useful properties related to packaging. For example, the composite can have organic or inorganic layers for enhanced gas and moisture barrier properties, a heat seal layer for forming a heat sealable container such as a bag, and/or a substrate layer suitable for receiving an adhesive either by coating or laminating.
Interest in an improved clear packaging film suitable for food products has been developing recently to satisfy consumers' strong desire to see the product within a package being purchased. It is frequently important for the packaging films to have good moisture vapor and oxygen gas barrier properties to maintain freshness of product, especially for sensitive, perishable goods such as food items. BOPP and BOPET film can be coated with very thin layers of metal, such as aluminum to cost effectively enhance barrier properties. However, metalized films with good barrier properties are typically not sufficiently transparent. While such film also can protect light sensitive product from photo-degradation it prevents viewing package contents. Thus there is a continuing need for clear packaging film that provides very good resistance to transmission of water vapor or oxygen gas with either no metallization or optionally ultra thin, non-hazy or non-opaque metallization. Commercial clear metalizing techniques such as aluminum oxide or silicon oxide can provide some gas barrier protection, but are known to make the film very brittle with poor resistance to flex cracking.
It is well known that polyvinyl alcohol (PVOH), ethylene vinyl alcohol copolymer (EVOH) or blends thereof can be applied to packaging films as a moisture vapor and oxygen transmission resistant layer. It is commonly used on BOPP and BOPET base layers in multilayer packaging films. Advantageously, the PVOH or EVOH layer is clear so that the packaging film can be transparent. Unfortunately, polyolefin or polyester packaging film coated with a PVOH or EVOH barrier layer has not been found to provide high quality of moisture vapor and oxygen resistance desired for products that are very sensitive or need to be stored for extended durations. In addition, high humidity conditions can cause PVOH or EVOH coatings to absorb moisture or swell which can reduce gas barrier effectiveness.
There remains need to have a clear packaging film with good physical properties for strength and film handling purposes and that also has excellent moisture vapor and oxygen transmission resistance. It is much desired to have a clear BOPP or BOPET film that has very good barrier properties. A great need exists for clear, BOPP or BOPET film that can be produced cost competively with existing films and has oxygen transmission resistance comparable or better than PVOH or EVOH barrier coated packaging films. It is particularly desirable to have highly oxygen and moisture vapor transmission resistant film for packaging of snack foods.